Enhancing the electrical conductivity of 3D printed continuous carbon fibre reinforced composites via surface coating of MWCNT on filaments

3D printed composites incorporating multi-walled carbon nanotubes (MWCNT) have generated significant research interests due to their multifunctionality . Melt mixing of MWCNT with polymers has been widely used to fabricate feedstocks for 3D printing . However, this approach cannot be applied to continuous fibre filaments because the process itself would damage the continuous fibres. Therefore, a layer-by-layer coating process was developed in the current work to coat continuous fibre filaments with MWCNT. Water dispersed MWCNT were prepared with the aid of poly sodium 4-styrene-sulfonate (PSS) and deposited onto the surface of the continuous carbon fibre filament (CFF) by implementing a layer-by-layer self-assembly technique. Scanning electron microscopy (SEM) observations showed that the amount of MWCNT deposited increased with the number of coating layer. A good coverage of MWCNT on the surface of CFF was achieved with coating of three-layers or more. Compared with uncoated filaments, the electrical conductivity of the filaments with three-layers and five-layers showed a 31% increase. Subsequently, the MWCNT-coated CFF were used on a Markforged® printer and printed out. The addition of MWCNT was found to enhance the electrical conductivity of the 3D printed specimens. However, the conductivity increase in the longitudinal, transverse and through-thickness directions was highly anisotropic , with over ten folds increase in the longitudinal direction compared with specimens without MWCNT. In addition, the bridging effect of MWCNTs was observed between the 3D printed fibre tows, which created shorter pathways for the electrons to pass through with less resistance, resulting in an increase in conductivity.